The present invention is directed to a time perception test instrument for performing a self-administered time perception test by a subject. This test may also be thought of as a test of cognition by the subject. It has been shown that individuals with impairment of cerebral function may show impairment in their ability to perceive or respond to time. Specifically, it has been shown that uremic toxicity may be determined using a time perception test which may be self-administered by the patient. The time perception test instrument of the present invention may be, therefore, used as an automated aid to scheduling artificial kidney treatment by measuring the mental performance decrement as well as providing an assesment of any other factors which may cause either permanent or temporary organic impairment of cerebral function.
Chronic intermittent hemodialysis is currently maintaining life in otherwise terminal uremics suffering from kidney disease. Unfortunately, the treatment intervals are usually determined empirically or scheduled to be convenient to the hospital personnel. The difficulties are that insufficient dialysis presents the risk of long term, low grade toxemia. On the other hand, with excessive dialysis, there is the added risk of the dialysis procedure itself, plus the additional cost. As mental toxicity is an early manifestation of the uremic state, the use of physchodynamic performance tests, such as the time perception test of the present invention, to objectively indicate the level of toxicity and the need for dialysis, is of great value in scheduling dialysis.
Assesment of the severity of uremia and the adequacy of the therapy for this condition is hampered today by the lack of sensitive, accurate and easily performed measurements of uremic toxicity. Although many chemical tests have been proposed, and have actually been used to asses clinical status in renal failure, these tests may not reflect physiological or behavioral changes in the uremic patients, which changes may be very subtle. Moreover, these tests must be performed by a trained technician and take time and cost money to perform. Also, the tests usually require a blood sample and the constant taking of blood could endanger the use of the vein for dialysis. It has been determined that several parameters of neurological function are altered in uremia and it has been recommended that a measurement of the degree of alteration may be used to assess the severity of uremic toxicity. However, the previous tests for quantitatively assessing the abnormality is often limited by insensitivity, poor reproducibility, the need for complex and expensive machinery, and the requirement for constant attendance by a well trained technician.
As indicated above, perception of short-time intervals is altered in a variety of conditions that effect the central nervous function even though some of these factors exhibit only subtle effects on other aspects of brain function. The present invention is, therefore, an apparatus to measure this cerebral function by a simple, easily repeatable, self-administered test. Specifically, the invention is directed to apparatus which measures a subject's ability to detect the presence or absence of equality in duration of a series of sequential periods between brief flashes of light. The apparatus of the present invention is an improvement on earlier devices which have been described in the literature and, specifically, the present invention includes a significant improvement over these earlier devices.
In the devices of the prior art, the test subject is presented with an array of flashing lights, all of which flash at irregular intervals except one. The test subject has to choose the one flashing light which is flashing at a regular rate. After the selection, a new light is randomly selected to be regular with the remaining lights flashing at an irregular rate. The present invention provides an improvement over the prior art devices since the test provided by the present invention is not too difficult and is a true test for the measuring of mental performance decrement. The test provided by the present invention is not tedious and fatiguing for the test subject and does not create extraneous barriers to the test being one of a true test of mental impairment. With the test provided by the present invention it is simple to orient the test subject and it is not necessary that technical personnel be available so that the test is truly self-administered. The present invention also includes an automatic time penalty, which records a completed trial and randomly chooses a new irregular light if the test subject does not make a selection within a predetermined period of time.
The present invention provides a test subject with a completely opposite task to that of the prior art devices, i.e., choosing from an array of lights wherein only one light is flashing at an irregular rate. This choosing of the one light flashing at an irregular rate has been found to be significant improvement over the prior art devices, since it is truly a test of mental impairment. Moreover, the present invention includes a number of other improvements so that the time perception test instrument of the present invention is a more useful instrument for the assessment of central nervous system function.
The test subject is presented with nine intermittently illuminated pushbuttons mounted in an array and with eight of the buttons flashing at closely regular intervals but asynchronously with a particular pattern such as 0.1 seconds on and 0.6 seconds off and up to .+-. 10 percent. The slight differences between the regular oscillator prevents the regularly flashing lights from flashing in a regular pattern so that the test subject could pick out the irregularly flashing light through a pattern recognition and some method should be used, such as the above, so that the oscillators are asynchronous relative to each other, so as to prevent pattern recognition. One of the illuminated pushbuttons, which is randomly changed after each selection by a test subject, flashes in an irregular sequential pattern, such as 0.1 seconds on and 0.4 seconds off, 0.1 seconds on, and 0.8 seconds off, etc. The degree of irregularity of the irregularly flashing buttons may be controlled by a manual control means. The test subject is requested to examine each lighted pushbutton in turn, and to press the particular button which appears to the test subject to be the irregularly flashing lighted button. After each selection by the test subject or after a predetermined period, such as 45 seconds, whichever occurs first, the test instrument omits an audible signal, records a completed trial, and, again, randomly selects one lighted pushbutton to flash irregularly. The number of trials and the number of correct selections may be read from a digital display and this digital display may be hidden from view of the test subject by a lockable means. When a predetermined number of trials, such as 10 trials, are completed, all of the lights are turned off.
The display generator consists of 9 regular oscillators corresponding in number to the pushbuttons, one irregular oscillator, and a random number generator. The random number generator consists of a rapidly cycled zero-to-eight counter that is briefly activated each time the instrument is turned on, one of the lighted buttons is pressed, or after the predetermined period, such as 45 seconds, have elapsed with no selection by the test subject. This random number generator determines which of the nine lights is to be driven by the irregular oscillator and, in particular, selects a particular gate to pass the output of the irregular oscillator rather than the output of a regular oscillator associated with the gate.
The random generator also determines which one of a plurality of coincidence detectors may provide an output signal, so that a count is entered in a correct score counter when the correct lighted button is pressed. A separate circuit records the total number of times a selection of a lighted button is made, including the number of times that the predetermined period of time, such as 45 seconds, has elapsed without a selection. All of the lights may be turned off at the end of a predetermined number of tests, such as ten trial selections. A test subject can learn to operate the instrument and self-administer the test after a short period of instruction. The control of irregularity of the irregular oscillator may be manipulated by the technician to aid in the learning cycle of the instrument. Specifically, the degree of irregularity may be controlled to be quite severe so that it is obvious to the test subject which of the lights is flashing in an irregular pattern and with the degree of irregularity controlled to be closer to the regularly flashing lights so as to make the test more severe. Also, the audio output may be coupled to the irregular oscillator and one of the regular oscillators through a switch, to provide an audio output corresponding to the flashing of the lights. This may help the test subject to understand the difference between the outputs of the oscillators.
It should be appreciated that although the test instrument is described with reference to a measurement of uremic toxicity, the instrument may also be useful for objective measurements in a variety of conditions, including brain tumors and the effects of toxic materials, such as drugs and alcohol.